Acid cooked pigskin gelatins for photographic subbing



sirable for the purpose.

United ttes atent 1 2,992,213 ACID COOKED PIGSKIN GELATINS FORPHOTOGRAPHIC SUBBING John W. Gates, Jr., Paul E. Miller, Robert R.Phillips, and Gale F. Nadeau, all of Rochester, N.Y., assignors toEastman Kodak Company, Rochester, N.Y., a corporation of New Jersey NoDrawing. Filed Nov. 8, 1957, Ser. No. 695,205 Claims. (Cl. 260-117) Thisinvention relates to the treatment of acid cooked pigskin gelatin toadapt it to use for subbing photographic film base and the subbed filmbase and film obtained by its use.

In the manufacture of photographic film the finished product ordinarilyconsists of a transparent film base of a polymeric material such ascellulose acetate, cellulose acetate propionate, polystyrene, polyester,or the like, containing a layer of silver-halide-gelatin photographicemulsion thereon. To facilitate good adherence of the emulsion layer tothe film base subbing layers are usually employed, of which gelatin isone of the important constituents. It is desirable that the gelatinemployed have certain properties which make it suitable for thispurpose. For instance, the gelatins usable as subbing materials in thepreparation of photographic film bases should (1) Produce stabledispersions in the mixed solvents which are employed for applying thecoatings thereto; g

(2) Produce subbing layers which will not allow stripping off of theemulsion layer either wet or dry and exhibit a high bonding strength toboth the film base and the emulsion layer;

(3) Produce subbing layers having a high clarity and a minimum of color;

(4) Produce subbing layers with no wet haze. There are other propertiesof importance to this use such as photographic inertness to the emulsionlayer applied thereon.

The gelatins which are ordinarily employed for subbing purposes havebeen developed by long years of experience and trial and are generallyprepared from limed cattle hides and calf skins and are of necessity ofvery low ash content so as to obtain good compatability and dispersionin the mixture of non-aqueous solvents Which may be employed in applyingthe same to photographic film base.

The gelatins obtained from pigskins have been considered in thisconnection due to the generally high jelly strength of those gelatins.High jelly strength indicates that the gelatin has good adhesion to thefilm base.

-However, When deashed pigskin gelatins produced by means of thecustomary acid cooked procedure or those from limed pigskins have beenemployed for photographic layers the light transmission of thosegelatins has been poor and their compatibility with mixed solvents asemployed for subbing has not been considered satisfactory. Therefore,even though gelatins having a jelly strength above 260 grams shoom arereadily obtained from pigskins either by a first run extraction or by asecond run extraction thereof, nevertheless, those gelatins have shownproperties which were not considered de- Ordinarily in the obtaining ofgelatin from pigskins the acid cook procedure is employed which involvesthe extraction of gelatin with water at a pH within the range of 4-5.After the grease has been removed from the extractant thus obtained theresulting gelatin in aqueous solution can be made to gel by coolinggiving products having a jelly strength above 260 shoom. It is to theuse of those gelatins that the present invention is directed.

One object of our invention is to provide a procedure for treatingpigskin gelatin to adapt it for use in subbing layers employed in thepreparation of photographic films. Another'object of our invention is toprovide a gelatin from pigskin which will give layers when applied totransparent polymeric sheeting having a high bonding strength thereto,whether in wet or dry condition. A further object of our invention is toprepare from high jelly strength pigskin gelatin a product whichpossesses good light transmission properties and the capacity for givingsmooth layers when coated out from its solution in mixed solvents onto asupport therefor; other objects of our invention will appear herein.

We have found that acid cooked pigskin gelatins of high jelly strengthcan be adapted to use for subbing purposes in the manufacture ofphotographic film if that gelatin is given an alkaline treatment withincertain critical temperatures and pH ranges. The treatment of thepigskin gelatin which should have a jelly strength of at least 260 gramsshoom may be with either aqueous am-' monia or with alkaline alkalimetal compounds such as alkali metal hydroxide or alkali metalcarbonate, for instance, sodium hydroxide, potassium hydroxide, sodiumcarbonate or the like. The treatment of the gelatin is carried out byleaching for a time such as 1-6 hours with the aqueous alkaline solutionat a pH within the range of 8-9.5 and a temperature of 35-55 F. Thelength of time employed for this treatment may vary with the individualoperator. The effectiveness of the treatment is the. criterion of thelength of time which one will wish to employ. We have found that a 4hour treatment is ordinarily sufiicient in every situation but ifshortening of the time is desirable, in some cases the time used maybeas little as 1 hour and a satisfactory product may be obtained. Afterthe treatment of the gelatin with the alkaline liquor it maybe employeddirectly for the subbing layers particularly following the ammoniatreatment or it may be subjected first to a deashing treatment withaqueous acetic acid as is well known in the art, the latter ordinarilybeing desirable where the treatment of the gelatin has been withalkaline alkali metal compound solutions. After the gelatin has beentreated either with.

the alkaline solution or with the combination of alkaline solution anddeashing it is then thoroughly washed to remove water soluble salts orthe like which might be present therein. using several changes of coldwater which may involve 3 or 4 or more washings of the gelatin. Althoughit appears that the use of distilled or demineralized water in thealkaline treatment or in the washing operation or both produces a betterproduct than where tap water is employed, nevertheless, the use of tapwater in these operations has been found to be effective and its use isalso included within the scope of the invention which we have made. Toobtain gelatin of the best jelly strength the first run type of gelatinsmay be employed but many second run gelatins have a jelly strength above260 grams shoom and may be employed in the coating of subbing layers orin admixture with first run gelatin for that purpose. It has been notedthat the acid which has been employed in preparing the pigskin gelatinmay be any one of several acids; for instance, acids such ashydrochloric, sulfuric, acetic or the like may be employed and theextracted gelatins obtained will be substantially equivalent incharacteristics.

The ammonia treatment of the gelatin may be carried out by plumping thegelatin such as in the form of flakes or noodles approximately 4 hoursin cold water which has been adjusted to a pH of 8.5 with ammonia andfollowing this treatment the gelatin may then be subjected to successivetreatments with cold water, each treatment being of approximately 4hours duration. The gelatin may then be melted if desired, and treatedwith acetic This Washing operation is carried out acid, or may beemployed without such treatment. In this treatment tap water may be usedparticularly if the gelatin employed is a first run pigskin gelatin or ablend of first and second run gelatins in which the first run gelatinpredominates. lt is preferable when the gelatin treated is a second rungelatin that the water treatment be confined to the use of distilledwater or demineralized water such as is obtained by the treatment ofwater with a zeolite or a Permutit base exchange resin.

Instead of the ammonia treatment the acid cooked pigskin gelatin maytreated for 4 hours in cold water adjusted to a pH such as of 9 to 9.5with sodium hydroxide. The gelatin can then be washed in water such asfor 2 hours and deashed by treatment with changes of dilute aqueousacetic acid prepared with either demineralized Water or with tap water.This treatment is useful for the treatment of either first run gelatin,second run gelatin or a mixture of first and second run gelatinsextracted from acid cooked pigskin providing of course that the jellystrength of the gelatin is above 260 grams shoom.

The pigskin gelatins obtained by the alkaline treatments described aresuitable for use in any of the accepted formulas for coatingcompositions for the application of subbing formulas for coatingcompositions for the application of subbing layers to film supportswhich compositions include gelatin therein. The layers thus obtainedexhibit good light transmission properties and give smooth surfaces whencoated out as subbing layers indicating the good compatibility of thegelatin for the solvent mixtures which are employed in preparing thecoating compositions.

The following examples illustrate the treatment of acid cooked pigskingelatins to render them useful for subbing purposes and typical subbingoperations in which those gelatins have been used to give layers of goodproperties.

Example 1 2 pounds of a second run acid cooked pigskin gelatin wasimmersed in 20 liters of 0.1% sodium hydroxide solution having atemperature of 40-45 F. for 2 hours with occasional stirring. The liquidwas drained from the gelatin and a second addition of 20 liters of cold0.1% sodium hydroxide solution was added to the gelatin and the mixturewas stirred occasionally over a 2 hour period. The 0.1% sodium hydroxidesolution had a pH within the range of 9-9.5. The liquid was drained fromthe gelatin and the gelatin was washed with distilled water with 3 onehour changes. The gelatin was then deashed with aqueous acetic acid anddried in a current of warm dry air.

The deashed gelatins which were employed as starting materials inseveral runs as described in Example 1 had light transmissions of 46.1%,51.2% and 37.2%. After those gelatins were treated by the proceduredescribed in Example 1 they exhibited light transmissions of 77.8%,64.4% and 72.2%. When first run acid cooked pigskin gelatins wereemployed in such a procedure which gelatins when deashed had lighttransmissions of 45.2%, 37.8% and 53.4% they exhibited after thetreatment as described in Example 1 light transmissions of 78.2%, 61.6%and 74%. Pigskin gelatins which had not been deashed could not be testedfor light transmission because those gelatins would not even disperse inthe solvents employed for the subbing procedure. The light transmissionis determined by measuring the amount of light transmitted by subsolutions made with the various gelatins which values are all determinedunder the same conditions.

Example 2 2 /2 pounds of pigskin gelatin in noodle form were leached for4 hours with 20 liters of water having a temperature of 40 F., the pH ofthe water being adjusted to 8.5 with 28% aqueous ammonia. Over the timeof treatment the pH was maintained at 8.5 by occasional. am-

monia additions. The water was then drained from the gelatin and thelatter was washed with four 4 hour 20 liter leaches with cold water.Some of the gelatin was dried by means of a current of warm dry air. Theremainder of the gelatin was melted into solution, the pH thereof wasadjusted to 4.65 with acetic acid and the mass was chilled and dried.The light transmission values of the gelatins thus obtained were foundto be considerably improved over those of acid cooked pigskin gelatinswhich had not been given an alkaline treatment in accordance with ourinvention. It was noted that when subbing layers of pigskin gelatin inaccordance with our invention were applied to photographic film basethat the pigskin gelatin layers were characterized by 100% resistance tostripping of the emulsion from the photograph film base whereas in manycases of gelatins of other types having jelly strengths below 260 gramsshoom stripping of the emulsion from the film base occurred.

Example 3 A batch of first run acid cooked pigskin gelatin was treatedwith successive amounts of cold tap water sufficient in each treatmentto thoroughly cover the gelatin. The gelatin which was in the form offlakes was stirred occasionally in each step. In the first step ammoniahad been added to the water to hold the pH at 8.5 and the A batch offirst run acid cooked pigskin gelatin in flake form was treated withseveral successive changes of cold demineralized water which water had aminimum of 500,000 ohms resistance. In the first two water treatmentssufficient sodium hydroxide had been added to hold the pH at 9.5 and themass was stirred for 2 hours in each of the steps. After removal of thealkaline treating liquid from the gelatin flakes they were immersed inwater and stirred for 3 hours. The water was removed and the gelatin wassubjected to 7 successive changes of water in each case containingsufficient acetic acid to reduce the pH to 4-5. In each of thesetreatments the mass was stirred for 1 hour. The gelatin flakes were thenremoved and were dried on nets in the air. The gelatin obtained wasfound to have good light transmission properties, gave good smoothsurfaces when employed in the form of subbing layers, and thephotographic film prepared using this gelatin as at least one subbinglayer exhibited high resistance to emulsion stripping.

The following examples are subbing compositions in which acid cookedpigskin gelatins have first been treated by procedures in accordancewith our invention.

Example 5 triacetate film support while it was maintained at aternpcrature of F. by means of a water tempered subbing drum. The subcoated support thus obtained was employed for preparing photographicfilm by coating silver halide-gelatin photographic emulsion thereon.This emulsion layer when driedwas found to be firmly bonded to .the filmsupport.

B. Aphotographic filmsupport was prepared by coaling cellulosetriacetatefilm support with a subbing composition as described in A andthere was then applied to this surface an overooating layer of thefollowing composition: 0.25% if deashed acid cooked pigskingelatin whichhad been treated in accordance with our invention, 0.25% of glacialacetic acid, 40% of methyl alcohol, of butyl alcohol and 49.5% of water.The subbed film support was kept at a temperature of 150 F. and theovercoat solution was also heated to this temperature and applied to thesub layer under these conditions. The product obtained was coated with asilver halide-gelatin photographic emulsion layer and that layer wasfound to be firmly bonded to the film support.

Example 6 This example illustrates the use of acid cooked pigskingelatin treated as described herein for the preparation of compositionsto apply subbing layers to film supports of cellulose acetate butyrateand cellulose acetate propionate.

A. A composition was prepared consisting of 1.25% acid cooked pigskingelatin treated as described herein, 3% of sub type cellulose nitrate,1% of glacial acetic acid, chromic chloride in an amount 1.5% by weightof the gelatin used, 50% acetone, 4% water and the balance methylalcohol. The subbing layer was applied to a cellulose acetate butyratefilm support by the bead method during which application the surfacetemperature of the support was maintained at 50 F. The resulting subbedfilm support was overcoated with a gelatin-silver halide emulsion whichemulsion layer was found to be firmly bound to the cellulose acetatebutyrate base.

B. Cellulose acetate butyrate support was coated as described in A andthis subbed film support was then overcoated with an overcoating layerapplied from a composition as deson'bed in B of the preceding example.To the subbed film base was applied on the subbed side of agelatin-silver halide photographic emulsion. The emulsion layer wasfound to be firmly bound to the fihn support.

Example 7 This example relates to the preparation of polystyrene filmsupport for the application of photographic emulsion layer thereto byapplying thereto at least one subbing layer containing pigskin gelatintreated in accordance with the invention.

To a polystyrene film support having a temperature of 75 F. was applieda layer using the following composition: 2.25% n-butyl methacrylate,2.25% isobutyl methacrylate, 25% methyl alcohol, 25% n-butyl alcohol and65.5% hexane. Over this subbing layer a layer was applied while thesupport was held at 75 F. of the following composition: 2.5% cellulosenitrate, 10% methyl Cellosolve, 5% n-bu-tyl alcohol, and 82.5% methylalcohol. There was then applied to the film support at 100 F. over thislayer a layer from a composition as follows: 1.2% acid cooked pigskingelatin which had been treated as described herein, 0.2% cellulosenitrate, 1.0% glacial acetic acid, chro-mic chloride in an amount 1.5%by weight of the gelatin, 10% of methyl cellosolve, 20% of water and thebalance methyl alcohol. Each of these layers was applied by the beadmethod and the subbing layers were each dried before application of thesucceeding sub layer. There was then applied to the subbed polystyrenefilm support a gelatin-silver halide photographic emulsion. The emulsionlayer thus applied was found to be firmly bound to the polystyrene filmsupport.

Example 8 There was applied to a polyethylene glycol tereph- 6 thalatefilm support a layer of a resin latex consisting .of a hydrosol obtainedby polymerizing together 2 parts of itaconic acid, 15 parts ofmethylacrylate and 82 parts of vinylidene chloride. After drying thecoated film was stretched 200% in both a lengthwise and crosswisedirection and was then crystallized by means of heat. The subbedpolyester film support was then overcoated with a composition consistingof 0.5% acid cooked pigskin gelatin which had been treated as describedherein, 0.015% of a 10% solution of cetyl betaine, 0.017% of a 10%solution of chrome alum, 0.25% of urea and the balance water. The thussubbed polyester film support was heat cured for approximately 5 minutesat 250 F. There was then applied to the subbed polyester film support alayer of a photosensitive gelatin silver halide photographic emulsion.The emulsion layer was found to be firmly bound to the film support.

The firmness with which an emulsion layer is bound to film support istested by a wet stripping test procedure in which the film is exposed tolight and developed, fixed and washed as recommended for thephotographic emulsion used. After washing the soft swollen emulsion isscored with .a sharp pointed instrument and an attempt is thereupon madewith the tips of the fingers to remove the emulsion from the film baseby rubbing across the score marks. In addition an attempt is made toremove the emulsion from the cut edge of wet processed film by rubbingwith the balls of the fingers. In the case of photographic filmsincluding the use of subbing layers containing acid cooked pigskingelatin which had been treated under the conditions of the inventiondescribed herein the emulsion layers were found to be resistant to thiswet stripping procedure both when tested at the score marks and whentested at the cut edge of the sample.

We claim:

1. A method of treating acid cooked pigskin gelatin to adapt it forphotographic subbing purposes which comprises leaching acid cookedpigskin gelatin having high jelly strength with aqueous alkali selectedfrom the group consisting of the aqueous solutions of ammonia and ofalkaline alkali metal compounds for 1-6 hours at a pH of 8-9.5 and atemperature within the range of 35-55 F. followed by washing to removethe alkali.

2. A method of treating acid cooked pigskin gelatin to adapt it for usefor photographic subbing pmposes which comprises leaching pigskingelatin having high jelly strength with aqueous ammonia for 1-6 hours ata pH of 8-9.5 and a temperature within the range of 35-55 F. followed bywashing to remove the alkali.

3. A method of treating acid cooked pigskin gelatin to adapt it for usefor photographic subbing purposes which comprises leaching acid cookedpigskin gelatin having high jelly strength with an aqueous alkalinealkali metal compound for 1-6 hours at a pH of 8-9.5 and a temperaturewithin the range of 35-55 F. followed by washing to remove the alkali.

4. A method of treating acid cooked pigskin gelatin to adapt it for usefor photographic subbing purposes which comprises leaching acid cookedpigskin gelatin having high jelly strength with aqueous alkali selectedfrom the group consisting of the aqueous solutions of ammonia and ofalkaline alkali metal compounds for 1-6 hours at a pH of 8-9.5 and at atemperature within the range of 35-5 5 F., and subsequently treating theleached gelatin with aqueous acetic acid and washing the thus treatedgelatin with water.

5. A method of treating acid cooked pigskin gelatin to adapt it for usefor photographic subbing purposes which comprises leaching acid cookedpigskin gelatin having high jelly strength with aqueous alkali selectedfrom the group consisting of the aqueous solutions of ammonia and ofalkaline alkali metal compounds for l-6 hours at a pH of 89.5 and at atemperature Within the range of 35-55 F., and subsequently treating theleached 7 gelatin with aqueous acetic acid and washing the thus2,351,174 treated gelatin with demineralized water. 2,398,004 2,598,608Reiereuges Cited in the file of this patent 2,834,771

UNITED STATES PATENTS 5 1,865,497 Atwood July 5, 193 625,873

8 Whitehead June 13, 1944 Houck et a1. Apr. 9, 1946 Sale May 27, 1952Mitchell et a1. May 13, 1958 FOREIGN PATENTS Great Britain July 5, 1949

1. A METHOD OF TREATING ACID COOKED PIGSKIN GELATIN TO ADAPT IT FORPHOTOGRAPHIC SUBBING PURPOSES WHICH COMPRISES LEACHING ACID COOKEDPIGSKIN GELATIN HAVING HIGH JELLY STRENGTH WITH AQUEOUS ALKALI SELECTEDFROM THE GROUP CONSISTING OF THE AQUEOUS SOLUTIONS OF AMMONIA AND OFALKALINE ALKALI METAL COMPOUNDS FOR 1-6 HOURS AT A PH OF 8-9.5 AND ATEMPERATURE WITHIN THE RANGE OF 35-55* F. FOLLOWED BY WASHING TO REMOVETHE ALKALI.